A low threshold for North Atlantic ice rafting from "low-slung slippery" late Pliocene ice sheets

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doi: 10.1029/2009PA001736
Author(s): Bailey, Ian; Bolton, Clara T.; DeConto, Robert M.; Pollard, David; Schiebel, Ralf; Wilson, Paul A.
Author Affiliation(s): Primary:
University of Southampton, National Oceanography Centre, Southampton, United Kingdom
Other:
University of Massachusetts at Amherst, United States
Pennsylvania State University, United States
Volume Title: Paleoceanography
Source: Paleoceanography, 25(1). Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0883-8305 CODEN: POCGEP
Note: In English. 71 refs.; illus., incl. 1 table, sketch map
Summary: Suborbital variability in late Pleistocene records of ice-rafted debris and sea surface temperature in the North Atlantic Ocean appears most extreme during times of enlarged ice sheets with a well-constrained benthic oxygen isotope-defined "ice volume threshold" (δ18OT) for the "100 ka (inter)glacial" world. Information on climate instability for the earlier Pleistocene and late Pliocene is more fragmentary and/or of much lower temporal resolution, but the data available suggest similar behavior with δ18OT remaining more or less constant over the past 3000 ka. This finding is puzzling because it implies that ice rafting is highly sensitive to ice volume on short (suborbital/glacial-interglacial) time scales but not to the long-term changes in ice sheet composition associated with intensification of Northern Hemisphere glaciation (NHG). Here we report new high-resolution records of stable isotope change and ice rafting in the North Atlantic at Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) during two glacials key to intensification of NHG (marine isotope stages G4, ∼2640 ka, and 100, ∼2520 ka). We find a pattern of suborbital ice rafting events showing clear evidence of threshold behavior. However, contrary to previous reports, we find that δ18OT for the late Pliocene is up to 0.45ppm Vienna Peedee belemnite (VPDB) lower than for the late Pleistocene. Using published Plio-Pleistocene global sea level records, we evaluate different potential explanations for this finding. We conclude that the observed Pliocene-Pleistocene offset in δ18OT is attributable to the existence of low-slung Pliocene ice sheets that flowed more readily than their late Pleistocene counterparts, associated with a smaller contemporaneous continental ice volume and less isotopically depleted ice.
Year of Publication: 2010
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Anomalinidae; Atlantic Ocean; Cassidulinacea; Cenozoic; Cibicidoides; Cibicidoides wuellerstorfi; Expeditions 303/306; Foraminifera; IODP Site U1308; IODP Site U1313; Ice rafting; Ice sheets; Integrated Ocean Drilling Program; Invertebrata; Isotope ratios; Isotopes; Leg 162; Mid-Atlantic Ridge; Neogene; North Atlantic; Northeast Atlantic; O-18/O-16; ODP Site 980; ODP Site 981; ODP Site 983; Ocean Drilling Program; Oxygen; Pliocene; Protista; Reykjanes Ridge; Rockall Bank; Rotaliina; Stable isotopes; Tertiary; Upper Pliocene
Coordinates: N495300 N495300 W0241400 W0241400
N602412 N602412 W0233826 W0233826
N552906 N552906 W0144208 W0144208
N410000 N410000 W0325700 W0325700
Record ID: 2010082337
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